It is well known in the art to use a control system to manage the limited power sources such as in trailer trucks for example. A standard power supply circuitry is currently commonly used but still suffers of inconvenient and potential drawbacks for the user. Alternator failure and starter motor failure are just examples that can be caused by an inappropriate use or control of the numerous accessories or power consumers necessary nowadays whilst operating and spending numerous hours in such trailer trucks. Accessories related to lighting, heating, communication equipment, food preparation, entertainment, etc. increased in number over the years and need to be monitored efficiently to avoid overloading the battery system that could cause failure of the batteries themselves.
Unlike most automobiles, commercial tractor/trailer vehicles typically utilize large diesel engines requiring substantial amounts of short-term power (e.g. about 1800 amperes) to start the engine. Such large current demands result from, among other things, the requirements of the fuel injection systems of such engines. In order to satisfy the large current demands of the diesel engines, commercial tractor/trailer vehicles are typically equipped with battery power systems including a plurality of high cold-cranking-ampere (CCA) batteries connected in parallel.
Supplying high cold-cranking current is not the only requirement for battery power systems used in commercial tractor/trailer vehicles. Such systems must also provide electrical power during times when the engine is not running. Of course, while the engine is running, ample electrical energy is usually provided by the alternator to operate such electrical devices as communication equipment, radios, lights, and other creature-comfort devices including microwave ovens, electric blankets, televisions, video tape recorders, etc. However, when the engine is not running, if any electrical devices are to be powered, they must be powered by the battery power system or an alternative system.
In earlier battery power systems, 12-volt batteries were utilized to both start the engine and run any electrical appliances when the engine was not running. Such systems experienced very significant problems, in that the electrical appliances would run the batteries down to the point that they would be unable to start the engine when required. This often occurred if the electrical appliances were run for a long period of time. In order to prevent this situation from occurring, systems were developed to isolate some batteries from the electrical appliances during times when the engine is not running. Those batteries would then be able to start the engine.
Presently, a so-called “3+1” battery power system is used to start the engine and power some electrical accessories when the engine is off. This system uses four pack 12-volt batteries which are typically enclosed in a battery box. Pack refers to the size and shape of the battery which is the industry standard for commercial tractor/trailers. To guarantee sufficient cold-cranking current, three of the pack 12-volt batteries are connected in parallel and used for starting the engine and for providing power at every critical electrical circuit such as computer, ignition circuit, etc. The remaining battery (the “+1” battery) is used exclusively for the key-off operation of some electrical accessories such as interior and exterior lights, heater, inverter, etc. When the engine is off, the accessory battery is isolated from the starting batteries. After the engine is started, the accessory battery is switched in parallel with the starting batteries so that it can be charged by the engine's alternator.
Although isolation power systems such as the 3+1 battery power system does not always ensure sufficient starting power by preserving the charge on the starting batteries, such systems work at the expense of providing power for electrical accessories while the engine is off. As a result, several alternatives have emerged to deal the limitations of these battery power systems. For example, a small minority of tractor/trailers are equipped with small diesel-powered generators to supply electrical energy to the appliances while the main diesel engine is off.
Where the tractor/trailer is not equipped with such generators as is the usual case, the drivers may elect to run the engine while they are resting or may choose to run the accessory battery down until it completely runs out of energy. Since running the engine is very expensive and potentially dangerous, many drivers choose to completely drain the accessory battery. Due to such repeated over-discharging, the accessory battery in a 3+1 battery power system cannot be fully recharged in many instances during normal operation of the vehicle. This causes a significant reduction of service life of the accessory battery. In fact, it is quite common for accessory batteries to need replacement every two or three months.
The fundamental problems are associated with 3+1 battery power systems: first, they fail to provide key-off power for an adequate amount of time such that durability of the battery is very poor. For example, during cold winter nights, a driver may depend on an electrical blanket to keep warm. If the driver decides to let the accessory battery run until it is low in energy, this will generally occur well before he or she is ready to drive again. Typically, the driver is going to let the electrical blanket run and the battery power level will get very low, close to a completely discharged state. Typically, the accessory battery is at a low state of charge when asked to provide power, which significantly reduces the time the driver may use the blanket. In such a case, the electrical blanket will cease to work during the night. This is obviously unacceptable. Second, 3+1 battery power systems can't ensure that the engine will always start. For example, the driver just needs to forget the ignition on, typically along with the computer, for the electrical consumer to completely drain down the batteries such that the truck/trailer won't start.
Numerous US patents relate to the isolation of the starter batteries from the rest of the vehicle electrical circuit such that they remain at an appropriate charge level to ensure proper starting of the engine whenever required. With such an isolation system, using an electronic controller coupled to high power relays, the starter batteries are prevented from being drained out or discharged by the different power consumers being turned on, especially when the engine is standby or not running and preserve their charge. Examples of such US patents are:                U.S. Pat. No. 6,765,312 granted to Urlass et al. on Jul. 20, 2004 entitled: “Dual Battery System”;        U.S. Pat. No. 6,731,021 granted to Urlass on May 4, 2004 entitled: “Two-Battery System”;        U.S. Pat. No. 6,597,149 granted to Urlass et al. on Jul. 22, 2003 entitled: “Battery System”;        U.S. Pat. No. 6,452,361 granted to Dougherty et al. on Sep. 17, 2002 entitled: “Battery System”;        U.S. Pat. No. 6,304,054 granted to Granberg et al. on Oct. 16, 2001 entitled: “Electrical System for Motor Vehicles”;        U.S. Pat. No. 6,232,674 granted to Frey at al. on May 15, 2001 entitled: “Control Device for a Vehicle Electric System”;        U.S. Pat. No. 6,229,279 granted to Dierker on May 8, 2001 entitled: “Dual Battery System”;        U.S. Pat. No. 6,222,341 granted to Dougherty et al. on Apr. 24, 2001 entitled: “Dual Battery Charge Maintenance System and Method”;        U.S. Pat. No. 5,986,431 granted to Hayes on Nov. 16, 1999 entitled: “Battery Power System for Vehicles”; and        U.S. Pat. No. 5,977,652 granted to Frey et al. on Nov. 2, 1999 entitled: “Device for Supplying Voltage in a Motor Vehicle Including Two Batteries and Having Improved Reliability”.        
In all of the above patents, the so-called vehicle electrical system battery, although isolated from the starter battery, is permanently connected to the vehicle electrical system. This permanent connection is not trouble free and could be the cause of the lost of all power batteries of a vehicle.
In fact, if such a vehicle electrical system battery becomes ever occurs to dry out or short for some reasons, it will draw most of the power generated by the alternator and will ultimately discharge the starter battery that would have been connected to the vehicle electrical system to assist the alternator and supply power to the consumers down to a level insufficient for ultimately restart the engine. In such a case, the driver of the tractor/trailer vehicle will end up being stuck without enough power to start the engine and drive to the closest location for costly repair and/or replacement of defect parts, after spending extensive time and money for towing.
Accordingly, there is a need for an improved isolated dual power source system for vehicle, with a relatively simple configuration.